Submersible pumps which have a motor-driven shaft that carries pump components are well known in the art. A prevalent problem with such pumps, however, is the overheating and failure of the internal motor and bearing components.
At one time, such components were immersed in an oil bath which was generally adequate to maintain the components cool enough to avoid failure while pumping water from a well to a remote location. However, with such oil-filled pumps, there is always the environmental and safety hazard of oil leaking into the well water.
As a result, more recently, internally confined water has replaced oil as the more standard cooling medium for submersible pumps. However, while such solves any environmental or safety problems, because the heat capacity of water is less than that of oil, the cooling efficiency of water-cooled pumps is far lower than that of oil-cooled pumps. Moreover, when water-cooled submersible pumps are operated at high speeds on a fairly continuous basis, the internal water churns so fast that, and is heated to the extent that, it may actually boil and turn to steam which, in turn, eliminates the hydrodynamic motor bearing film causing system failure.
In an effort to cool the internal water, some attempts have been made to circulate that water in the annulus between a hollow tube positioned in a hollow drive shaft. The warm water is pumped up in the annulus and is thereby exposed, near the top thereof, to the cooler well water. The circulating internal water then moves down the tube and back to the area of the hot motor. This elaborate system, while dissipating some heat, does not totally solve the problem and is not cost-effective.